Aberdeenshire Council has pledged to do all it can to open a school after six months.
Gartly School in Huntly has been shut since December following the discovery of an oil leak.
A spokesman for Aberdeenshire Council said: “We are continuing to do everything in our power to re-open Gartly School as soon as possible.
“The area the oil has affected and the associated remedial works required are more extensive than originally thought, now involving the demolition of outbuildings and replacement of soil underneath.
“Ultimately, colleagues in public health will decide when it is safe for pupils and staff to return to the building and samples to date have not enabled us to progress as we may have liked to.
“Our first priority remains the safety and wellbeing of children and staff.”